Tuesday, September 26, 2017

The Pierre Auger Collaboration, in which ASTRON is a partner, reports
observational evidence demonstrating that cosmic rays with energies a
million times greater than that of the protons accelerated in the Large
Hadron Collider come from much further away than from our own Galaxy.
These findings

Ever since the existence of cosmic rays with individual energies of
several Joules was established in the 1960s, speculation has raged as to
whether such particles are created there or in distant extragalactic
objects. The 50 year-old mystery has been solved using cosmic particles
of mean energy of 2 Joules recorded with the largest cosmic-ray
observatory ever built, the Pierre Auger Observatory in Argentina. It is
found that at these energies the rate of arrival of cosmic rays is ~6%
greater from one side of the sky than from the opposite direction, with
the excess lying 120˚ away from the Galactic centre.

In the view of Professor Karl-Heinz Kampert (University of Wuppertal),
spokesperson for the Auger Collaboration, which involves over 400
scientists from 18 countries, "We are now considerably closer to solving
the mystery of where and how these extraordinary particles are created,
a question of great interest to astrophysicists. Our observation
provides compelling evidence that the sites of acceleration are outside
the Milky Way”. Professor Alan Watson (University of Leeds), emeritus
spokesperson, considers this result to be “one of the most exciting that
we have obtained and one which solves a problem targeted when the
Observatory was conceived by Jim Cronin and myself over 25 years ago”.

Rare particles, gigantic detector

Cosmic rays are the nuclei of elements from hydrogen (the proton) to
iron. Above 2 Joules the rate of their arrival at the top of the
atmosphere is only about 1 per sq km per year, equivalent to one hitting
the area of a football pitch about once per century. Such rare
particles are detectable because they create showers of electrons,
photons and muons through successive interactions with the nuclei in the
atmosphere. These showers spread out, sweeping through the atmosphere
at the speed of light in a disc-like structure, similar to a
dinner-plate, several kilometres in diameter. They contain over ten
billion particles and, at the Auger Observatory, are detected through
the Cherenkov light they produce in a few of 1600 detectors, each
containing 12 tonnes of water, spread over 3000 km2 of Western
Argentina, an area comparable to that of Rhode Island. The times of
arrival of the particles at the detectors, measured with GPS receivers,
are used to find the arrival directions of events to within ~1˚.

An extragalactic origin

By studying the distribution of the arrival directions of more than
30000 cosmic particles the Auger Collaboration has discovered an
anisotropy, significant at 5.2 standard deviations (a chance of about
two in ten million), in a direction where the distribution of galaxies
is relatively high. Although this discovery clearly indicates an
extragalactic origin for the particles, the actual sources have yet to
be pinned down. The direction of the excess points to a broad area of
sky rather than to specific sources as even particles as energetic as
these are deflected by a few 10s of degrees in the magnetic field of our
Galaxy. The direction, however, cannot be associated with putative
sources in the plane or centre of our Galaxy for any realistic
configuration of the Galactic magnetic field.

Cosmic rays of even higher energy than the bulk of those used in this
study exist, some even with the kinetic energy of well-struck tennis
ball. As the deflections of such particles are expected to be smaller,
the arrival directions should point closer to their birthplaces. These
cosmic rays are even rarer and further studies are underway using them
to try to pin down which extragalactic objects are the sources.
Knowledge of the nature of the particles will aid this identification
and work on this problem is targeted in the upgrade of the Auger
Observatory to be completed in 2018. Source: Radboud University

Monday, September 25, 2017

This
artist's impression shows part of the cosmic web, a filamentary
structure of galaxies that extends across the entire sky. The bright
blue, point sources shown here are the signals from Fast Radio Bursts
(FRBs) that may accumulate in a radio exposure lasting for a few
minutes. The radio signal from an FRB lasts for only a few thousandths
of a second, but they should occur at high rates. Credit:M. Weiss/CfA.Low Resolution (jpg)

Cambridge, MA - When
fast radio bursts, or FRBs, were first detected in 2001, astronomers
had never seen anything like them before. Since then, astronomers have
found a couple of dozen FRBs, but they still don’t know what causes
these rapid and powerful bursts of radio emission.

For the first time, two astronomers from the Harvard-Smithsonian Center
for Astrophysics (CfA) have estimated how many FRBs should occur over
the entire observable universe. Their work indicates that at least one
FRB is going off somewhere every second.

"If we are right about such a high rate of FRBs happening at any
given time, you can imagine the sky is filled with flashes like
paparazzi taking photos of a celebrity," said Anastasia Fialkov of the
CfA, who led the study. "Instead of the light we can see with our eyes,
these flashes come in radio waves."
To make their estimate, Fialkov and co-author Avi Loeb assumed that
FRB 121102, a fast radio burst located in a galaxy about 3 billion light
years away, is representative of all FRBs. Because this FRB has
produced repeated bursts since its discovery in 2002, astronomers have
been able to study it in much more detail than other FRBs. Using that
information, they projected how many FRBs would exist across the entire
sky.

"In the time it takes you to drink a cup of coffee, hundreds of FRBs
may have gone off somewhere in the Universe," said Avi Loeb. "If we can
study even a fraction of those well enough, we should be able to unravel
their origin."

While their exact nature is still unknown, most scientists think FRBs
originate in galaxies billions of light years away. One leading idea is
that FRBs are the byproducts of young, rapidly spinning neutron stars
with extraordinarily strong magnetic fields.

Fialkov and Loeb point out that FRBs can be used to study the
structure and evolution of the Universe whether or not their origin is
fully understood. A large population of faraway FRBs could act as probes
of material across gigantic distances. This intervening material blurs
the signal from the cosmic microwave background (CMB), the left over
radiation from the Big Bang. A careful study of this intervening
material should give an improved understanding of basic cosmic
constituents, such as the relative amounts of ordinary matter, dark
matter and dark energy, which affect how rapidly the universe is
expanding.

FRBs can also be used to trace what broke down the "fog" of hydrogen
atoms that pervaded the early universe into free electrons and protons,
when temperatures cooled down after the Big Bang. It is generally
thought that ultraviolet (UV) light from the first stars traveled
outwards to ionize the hydrogen gas, clearing the fog and allowing this
UV light to escape. Studying very distant FRBs will allow scientists to
study where, when and how this process of "reionization" occurred.

"FRBs are like incredibly powerful flashlights that we think can
penetrate thise fog and be seen over vast distances," said Fialkov.
"This could allow us to study the 'dawn' of the universe in a new way."
The authors also examined how successful new radio telescopes – both
those already in operation and those planned for the future – may be at
discovering large numbers of FRBs. For example, the Square Kilometer
Array (SKA) currently being developed will be a powerful instrument for
detecting FRBs. The new study suggests that over the whole sky the SKA
may be able to detect more than one FRB per minute that originates from
the time when reionization occurred.

The Canadian Hydrogen Intensity Mapping Experiment (CHIME), that
recently began operating, will also be a powerful machine for detecting
FRBs, although its ability to detect the bursts will depend on their
spectrum, i.e. how the intensity of the radio waves depends on
wavelength. If the spectrum of FRB 121102 is typical then CHIME may
struggle to detect FRBs. However, for different types of spectra CHIME
will succeed.

The paper by Fialkov and Loeb describing these results was published in the September 10, 2017 issue of The Astrophysical Journal Letters, and is available online.

Headquartered
in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics
(CfA) is a collaboration between the Smithsonian Astrophysical
Observatory and the Harvard College Observatory. CfA scientists,
organized into six research divisions, study the origin, evolution and
ultimate fate of the universe.

These gaseous clouds, called planetary nebulae, are created when
stars in the last stages of life cast off their outer layers of material
into space. Ultraviolet light from the remnant star makes the material
glow. Planetary nebulae last for only 10,000 years, a fleeting episode
in the 10-billion-year lifespan of Sun-like stars.

The name planetary nebula has nothing to do with planets. They got
their name because their round shapes resembled planets when seen
through the small telescopes of the eighteenth century.

The Hubble images show the evolution of planetary nebulae, revealing
how they expand in size and change temperature over time. A young
planetary nebula, such as He 2-47, at top, left, for example, is small
and is dominated by relatively cool, glowing nitrogen gas. In the Hubble
images, the red, green, and blue colors represent light emitted by
nitrogen, hydrogen, and oxygen, respectively.

Over thousands of years, the clouds of gas expand away and the
nebulae become larger. Energetic ultraviolet light from the star
penetrates more deeply into the gas, causing the hydrogen and oxygen to
glow more prominently, as seen near the center of NGC 5315. In the older
nebulae, such as IC 4593, at bottom, left, and NGC 5307, at bottom,
right, hydrogen and oxygen appear more extended in these regions, and
red knots of nitrogen are still visible.

These four nebulae all lie in our Milky Way Galaxy. Their distances
from Earth are all roughly the same, about 7,000 light-years. The
snapshots were taken with Hubble's Wide Field Planetary Camera 2 in
February 2007. Like snowflakes, planetary nebulae show a wide variety of
shapes, indicative of the complex processes that occur at the end of
stellar life.

He 2-47, at top, left, is dubbed the "starfish" because of its shape.
The six lobes of gas and dust, which resemble the legs of a starfish,
suggest that He 2-47 puffed off material at least three times in three
different directions. Each time, the star fired off a narrow pair of
opposite jets of gas. He 2-47 is in the southern constellation Carina.

NGC 5315, the chaotic-looking nebula at top, right, reveals an
x-shaped structure. This shape suggests that the star ejected material
in two different outbursts in two distinct directions. Each outburst
unleashed a pair of diametrically opposed outflows. NGC 5315 lies in the
southern constellation Circinus.

IC 4593, at bottom, left, is in the northern constellation Hercules.

NGC 5307, at bottom, right, displays a spiral pattern, which may have
been caused by the dying star wobbling as it expelled jets of gas in
different directions. NGC 5307 resides in the southern constellation
Centaurus.

Saturday, September 23, 2017

Despite the advances made in past decades, the process of galaxy formation
remains an open question in astronomy. Various theories have been
suggested, but since galaxies come in all shapes and sizes — including elliptical, spiral, and irregular
— no single theory has so far been able to satisfactorily explain the
origins of all the galaxies we see throughout the Universe.

To determine which formation model is correct (if
any), astronomers hunt for the telltale signs of various physical
processes. One example of this is galactic coronas,
which are huge, invisible regions of hot gas that surround a galaxy’s
visible bulk, forming a spheroidal shape. They are so hot that they can
be detected by their X-ray emission, far beyond the optical radius of
the galaxy. Because they are so wispy, these coronas are extremely
difficult to detect. In 2013, astronomers highlighted NGC 6753, imaged
here by the NASA/ESA Hubble Space Telescope,
as one of only two known spiral galaxies that were both massive enough
and close enough to permit detailed observations of their coronas. Of
course, NGC 6753 is only close in astronomical terms — the galaxy is
nearly 150 million light-years from Earth.

NGC 6753 is a whirl of colour in this image — the bursts of
blue throughout the spiral arms are regions filled with young stars
glowing brightly in ultraviolet light, while redder areas are filled with older stars emitting in the cooler near-infrared.

With the help of the NASA/ESA Hubble Space Telescope, a German-led group of astronomers have observed the intriguing characteristics of an unusual type of object in the asteroid belt between Mars and Jupiter: two asteroids orbiting each other and exhibiting comet-like features, including a bright coma and a long tail. This is the first known binary asteroid also classified as a comet. The research is presented in a paper published in the journal Nature this week.

In September 2016, just before the asteroid 288P made its closest approach to the Sun, it was close enough to Earth to allow astronomers a detailed look at it using the NASA/ESA Hubble Space Telescope [1].

The images of 288P, which is located in the asteroid belt between Mars and Jupiter, revealed that it was actually not a single object, but two asteroids of almost the same mass and size, orbiting each other at a distance of about 100 kilometres. That discovery was in itself an important find; because they orbit each other, the masses of the objects in such systems can be measured.

But the observations also revealed ongoing activity in the binary system. “We detected strong indications of the sublimation of water ice due to the increased solar heating — similar to how the tail of a comet is created,” explains Jessica Agarwal (Max Planck Institute for Solar System Research, Germany), the team leader and main author of the research paper. This makes 288P the first known binary asteroid that is also classified as a main-belt comet.

Understanding the origin and evolution of main-belt comets — asteroids orbiting between Mars and Jupiter that show comet-like activity — is a crucial element in our understanding of the formation and evolution of the whole Solar System. Among the questions main-belt comets can help to answer is how water came to Earth [2]. Since only a few objects of this type are known, 288P presents itself as an extremely important system for future studies.

The various features of 288P — wide separation of the two components, near-equal component size, high eccentricity and comet-like activity — also make it unique among the few known wide asteroid binaries in the Solar System. The observed activity of 288P also reveals information about its past, notes Agarwal: “Surface ice cannot survive in the asteroid belt for the age of the Solar System but can be protected for billions of years by a refractory dust mantle, only a few metres thick.”

From this, the team concluded that 288P has existed as a binary system for only about 5000 years. Agarwal elaborates on the formation scenario: “The most probable formation scenario of 288P is a breakup due to fast rotation. After that, the two fragments may have been moved further apart by sublimation torques.”

The fact that 288P is so different from all other known binary asteroids raises some questions about whether it is not just a coincidence that it presents such unique properties. As finding 288P included a lot of luck, it is likely to remain the only example of its kind for a long time. “We need more theoretical and observational work, as well as more objects similar to 288P, to find an answer to this question,” concludes Agarwal.

Notes

[1] Like any object orbiting the Sun, 288P travels along an
elliptical path, bringing it closer and further away to the Sun during
the course of one orbit.

[2] Current research indicates that water came to Earth not via comets, as long thought, but via icy asteroids.

More InformationThe Hubble Space Telescope is a project of international cooperation between ESA and NASA.

The international team of astronomers in this study consists of
Jessica Agarwal (Max Planck Institute for Solar System Research,
Göttingen, Germany), David Jewitt (Department of Earth, Planetary and
Space Sciences and Department of Physics and Astronomy, University of
California at Los Angeles, USA), Max Mutchler (Space Telescope Science
Institute, Baltimore, USA), Harold Weaver (The Johns Hopkins University
Applied Physics Laboratory, Maryland, USA) and Stephen Larson (Lunar and
Planetary Laboratory, University of Arizona, Tucson, USA).

The results were released in the paper “A binary main belt comet” to be published in Nature.Image credit: NASA, ESA

Astronomers have used ALMA to capture a
strikingly beautiful view of a delicate bubble of expelled material
around the exotic red star U Antliae. These observations will help
astronomers to better understand how stars evolve during the later
stages of their life-cycles.

U Antliae [1] is a carbon star, an evolved, cool and luminous star of the asymptotic giant branch
type. Around 2700 years ago, U Antliae went through a short period of
rapid mass loss. During this period of only a few hundred years, the
material making up the shell seen in the new ALMA data was ejected at
high speed. Examination of this shell in further detail also shows some
evidence of thin, wispy gas clouds known as filamentary substructures.

This spectacular view was only made possible by the unique
ability to create sharp images at multiple wavelengths that is provided
by the ALMA radio telescope, located on the Chajnantor Plateau in
Chile’s Atacama Desert. ALMA can see much finer structure in the U
Antliae shell than has previously been possible.

The new ALMA data are not just a single image; ALMA
produces a three-dimensional dataset (a data cube) with each slice
being observed at a slightly different wavelength. Because of the Doppler Effect,
this means that different slices of the data cube show images of gas
moving at different speeds towards or away from the observer. This shell
is also remarkable as it is very symmetrically round and also
remarkably thin. By displaying the different velocities we can cut this
cosmic bubble into virtual slices just as we do in computer tomography
of a human body.

Understanding the chemical composition of the shells and
atmospheres of these stars, and how these shells form by mass loss, is
important to properly understand how stars evolve in the early Universe
and also how galaxies evolved. Shells such as the one around U Antliae
show a rich variety of chemical compounds based on carbon and other
elements. They also help to recycle matter, and contribute up to 70% of
the dust between stars.

Notes

[1] The name U Antliae reflects the fact that it is the fourth star that
changes its brightness to be found in the constellation of Antlia (The
Air Pump). The naming of such variable stars followed a complicated
sequence as more and more were found and is explainedhere.

More Information

This research was presented in a paper entitled “Rings and
filaments. The remarkable detached CO shell of U Antliae”, by F.
Kerschbaum et al., to appear in the journal Astronomy & Astrophysics.

The Atacama Large Millimeter/submillimeter Array (ALMA), an
international astronomy facility, is a partnership of ESO, the U.S.
National Science Foundation (NSF) and the National Institutes of Natural
Sciences (NINS) of Japan in cooperation with the Republic of Chile.
ALMA is funded by ESO on behalf of its Member States, by NSF in
cooperation with the National Research Council of Canada (NRC) and the
National Science Council of Taiwan (NSC) and by NINS in cooperation with
the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space
Science Institute (KASI).

ALMA construction and operations are led by ESO on behalf
of its Member States; by the National Radio Astronomy Observatory
(NRAO), managed by Associated Universities, Inc. (AUI), on behalf of
North America; and by the National Astronomical Observatory of Japan
(NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides
the unified leadership and management of the construction,
commissioning and operation of ALMA.

ESO is the foremost intergovernmental astronomy
organisation in Europe and the world’s most productive ground-based
astronomical observatory by far. It is supported by 16 countries:
Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland,
Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden,
Switzerland and the United Kingdom, along with the host state of Chile.
ESO carries out an ambitious programme focused on the design,
construction and operation of powerful ground-based observing facilities
enabling astronomers to make important scientific discoveries. ESO also
plays a leading role in promoting and organising cooperation in
astronomical research. ESO operates three unique world-class observing
sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO
operates the Very Large Telescope and its world-leading Very Large
Telescope Interferometer as well as two survey telescopes, VISTA working
in the infrared and the visible-light VLT Survey Telescope. ESO is also
a major partner in two facilities on Chajnantor, APEX and ALMA, the
largest astronomical project in existence. And on Cerro Armazones, close
to Paranal, ESO is building the 39-metre Extremely Large Telescope, the
ELT, which will become “the world’s biggest eye on the sky”.

Wednesday, September 20, 2017

A group-analysis of 30 exoplanets orbiting distant stars suggests that size, not mass, is a key factor in whether a planet’s atmosphere can be detected. The largest population-study of exoplanets to date successfully detected atmospheres around 16 ‘hot Jupiters’, and found that water vapour was present in every case.

The work by a UCL-led team of European researchers has important implications for the comparison and classification of diverse exoplanets. The results will be presented by Angelos Tsiaras at the European Planetary Science Congress (EPSC) 2017 in Riga on Tuesday 19th September.

“More than 3,000 exoplanets have been discovered but, so far, we’ve studied their atmospheres largely on an individual, case-by-case basis. Here, we’ve developed tools to assess the significance of atmospheric detections in catalogues of exoplanets,” said Angelos Tsiaras, the lead author of the study. “

This kind of consistent study is essential for understanding the global population and potential classifications of these foreign worlds.”
The researchers used archive data from the ESA/NASA Hubble Space Telescope’s Wide Field Camera 3 (WFC3) to retrieve spectral profiles of 30 exoplanets and analyse them for the characteristic fingerprints of gases that might be present. About half had strongly detectable atmospheres.
Results suggest that while atmospheres are most likely to be detected around planets with a large radius, the planet’s mass does not appear to be an important factor. This indicates that a planet’s gravitational pull only has a minor effect on its atmospheric evolution.

Most of the atmospheres detected show evidence for clouds. However, the two hottest planets, where temperatures exceed 1,700 degrees Celsius, appear to have clear skies, at least at high altitudes. Results for these two planets indicate that titanium oxide and vanadium oxide are present in addition to the water vapour features found in all 16 of the atmospheres analysed successfully.

“To understand planets and planet formation we need to look at many planets: at UCL we are implementing statistical tools and models to handle the analysis and interpretation of large sample of planetary atmospheres. 30 planets is just the start,” said Ingo Waldmann, a co-author of the study.

“30 exoplanet atmospheres is a great step forward compared to the handful of planets observed years ago, but not yet big-data. We are working at launching dedicated space missions in the next decade to bring this number up to hundreds or even thousands,” commented Giovanna Tinetti, also UCL.

The research at UCL has been funded by the Science and Technology Facilities Council (STFC) and the ERC projects ExoLights (617119) and ExoMol.
Results are summarized by Tsiaras et al. in the paper “A population study of hot Jupiter atmospheres,” which has been submitted to the Astrophysical Journal.

About the NASA/ESA Hubble Space TelescopeThe Hubble Space Telescope is a project of international cooperation between ESA and NASA.

About UCL (University College London)

UCL was founded in 1826. We were the first English university established after Oxford and Cambridge, the first to open up university education to those previously excluded from it, and the first to provide systematic teaching of law, architecture and medicine. We are among the world’s top universities, as reflected by performance in a range of international rankings and tables. UCL currently has over 39,000 students from 150 countries and over 12,500 staff. Our annual income is more than £1 billion.

The European Planetary Science Congress (EPSC) 2017 (www.epsc2017.eu) is taking place at the Radisson Blu Latvija in Riga, from Sunday 17 to Friday 22 September 2017. EPSC is the major European annual meeting on planetary science and in 2017 is hosted for the first time in the Baltic States. Around 800 scientists from Europe and around the world will attend the meeting and will give around 1,000 oral and poster presentations about the latest results on our own Solar System and planets orbiting other stars.

EPSC 2017 is organised by Europlanet and Copernicus Meetings. The Local Organising Committee is led by Baltics in Space, a not-for-profit organisation that is supporting 25 members centred around nine Baltic space facilities for the conference. The meeting is sponsored by Investment and Development Agency of Latvia, the Latvian Ministry of Education and Science, Latvijas Mobilais Telefons, Finnish Meteorological Institute, The Estonia-Latvia programme, The Representation of the European Commission in Latvia, the Planetary Science Institute, Latvijas Universitate and The Division for Planetary Sciences of the AAS.

Details of the Congress and a full schedule of EPSC 2017 scientific sessions and events can be found at the official website: http://www.epsc2017.eu/

Europlanet

Since 2005, the Europlanet project has provided European’s planetary science community with a platform to exchange ideas and personnel, share research tools, data and facilities, define key science goals for the future and engage stakeholders, policy makers and European Citizens with planetary science. Europlanet is the parent organisation of the European Planetary Science Congress (EPSC), and the EPSC Executive Committee is drawn from its membership.

The Europlanet 2020 Research Infrastructure (RI) is a €9.95 million project to address key scientific and technological challenges facing modern planetary science by providing open access to state-of-the-art data, models and facilities across the European Research Area. The project was launched on 1st September 2015 and has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 654208. Europlanet 2020 RI is led by the Open University, UK, and has 33 beneficiary institutions from 19 European countries.

The philosophy of the nonprofit organization, Baltics in Space, is to “Inventory, Identify, and Integrate” with a sprinkling of Inspiration to build a space product greater than the sum of its parts. The best resource in the space business is people. With an eye to strengthening the triple helix links (Industry, Education, Research), its planned outcomes are integrating Baltic-wide space events, compiling catalogs of skill-sets for prospective users and Baltic space project development with distributed teams and Baltic space education.

Tuesday, September 19, 2017

The new VLA Sky Survey (VLASS) sharpens the view. Here is the same radio-emitting object as seen, from left to right, with the NRAO VLA Sky Survey (NVSS), the FIRST Survey, and the VLASS. The VLASS image, unlike the others, allows astronomers to positively identify the image as jets of material propelled outward from the center of a galaxy that also is seen in the visible-light Sloan Digital Sky Survey. Technical data: NVSS image at 1.4 GHz in VLA's D configuration; FIRST image at 1.4 GHz in B configuration; VLASS image at 3 GHz in B configuration.
Credit: Bill Saxton, NRAO/AUI/NSF.Hi-res images

Images of the same celestial object from the NVSS, FIRST, and VLASS surveys, in order, showing increased resolution, or ability to discern detail.
Credit: Bill Saxton, NRAO/AUI/NSF.

New sky survey is largest observing project in VLA's history

Astronomers have embarked on the largest observing project in the more than four-decade history of the National Science Foundation’s Karl G. Jansky Very Large Array (VLA) — a huge survey of the sky that promises a rich scientific payoff over many years.

Over the next 7 years, the iconic array of giant dish antennas in the high New Mexico desert will make three complete scans of the sky visible from its latitude — about 80 percent of the entire sky. The survey, called the VLA Sky Survey (VLASS), will produce the sharpest radio view ever made of such a large portion of the sky, and is expected to detect 10 million distinct radio-emitting celestial objects, about four times as many as are now known.

“This survey puts to work the tremendously improved capabilities of the VLA produced by the upgrade project that was completed in 2012. The result will be a unique and extremely valuable tool for frontier research over a diverse range of fields in astrophysics,” said Tony Beasley, Director of the National Radio Astronomy Observatory (NRAO).

Astronomers expect the VLASS to discover powerful cosmic explosions, such as supernovae, gamma ray bursts, and the collisions of neutron stars, that are obscured from visible-light telescopes by thick clouds of dust, or that otherwise have eluded detection. The VLA’s ability to see through dust will make the survey a tool for finding a variety of structures within our own Milky Way that also are obscured by dust.

The survey will reveal many additional examples of powerful jets of superfast particles propelled by the energy of supermassive black holes at the cores of galaxies. This will yield important new information on how such jets affect the growth of galaxies over time. The VLA’s ability to measure magnetic fields will help scientists gain new understanding of the workings of individual galaxies and of the interactions of giant clusters of galaxies.

“In addition to what we think VLASS will discover, we undoubtedly will be surprised by discoveries we aren’t anticipating now. That is the lesson of scientific history, and perhaps the most exciting part of a project like this,” said Claire Chandler, VLASS Project Director.

The survey began observations on September 7. It plans to complete three scans of the sky, each separated by approximately 32 months. Data from all three scans will be combined to make sensitive radio images, while comparing images from the individual scans will allow discovery of newly-appearing or short-lived objects. For the survey, the VLA will receive cosmic radio emissions at frequencies between 2 and 4 GigaHertz, frequencies also used for satellite communications and microwave ovens.

NRAO will release data products from the survey as quickly as they can be produced. Raw data, which require processing to turn into images, will be released as soon as observations are made. “Quick look” images, produced by an automated processing pipeline, typically will be available within a week of the observations. More sophisticated images, and catalogs of objects detected, will be released on timescales of months, depending on the processing time required.

In addition, other institutions are expected to enhance the VLASS output by performing additional processing for more specialized analysis, and make those products available to the research community. The results of VLASS also will be available to students, educators, and citizen scientists.

Completing the VLASS will require 5,500 hours of observing time. It is the third major sky survey undertaken with the VLA. From 1993-1996, the NRAO VLA Sky Survey (NVSS) used 2932 observing hours to cover the same area of sky as VLASS, but at lower resolution. The FIRST (Faint Images of the Radio Sky at Twenty centimeters) Survey studied a smaller portion of sky in more detail, using 3200 observing hours from 1993 to 2002.

“The NVSS and FIRST surveys have been cited more than 4,500 times in scientific papers, and that number still is growing,” said Project Scientist Mark Lacy. “That’s an excellent indication of the value such surveys provide to the research community,” he added.

Since the NVSS and FIRST surveys were completed, the VLA underwent a complete technical transformation. From 2001-2012, the original electronic systems designed and built during the 1970s were replaced with state-of-the-art technology that vastly expanded the VLA’s capabilities.

“This upgrade made the VLA a completely new scientific tool. We wanted to put that tool to use to produce an all-sky survey that would benefit the entire astronomical community to the maximum extent possible,” Beasley said.

In 2013, NRAO announced that it would consider conducting a large survey, and invited astronomers from around the world to submit ideas and suggestions for the scientific and technical approaches that would best serve the needs of researchers. Ideas were also solicited during scientific meetings, and a Survey Science Group was formed to advise NRAO on the survey’s scientific priorities that includes astronomers from a wide variety of specialties and institutions.

Based on the recommendations from the scientific community, NRAO scientists and engineers devised a design for the survey. In 2016, a pilot survey, using 200 observing hours, was conducted to test and refine the survey’s techniques. The Project Team underwent several design and operational readiness reviews, and finally obtained the go-ahead to begin the full survey earlier this year.

“Astronomy fundamentally is exploring — making images of the sky to see what’s there. The VLASS is a new and powerful resource for exploration,” said Steve Myers, VLASS Technical Lead.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

For decades, astronomers have known about irregular outbursts from
the double star system V745 Sco, which is located about 25,000 light years
from Earth. Astronomers were caught by surprise when previous outbursts
from this system were seen in 1937 and 1989. When the system erupted on
February 6, 2014, however, scientists were ready to observe the event
with a suite of telescopes including NASA’s Chandra X-ray Observatory.

V745 Sco is a binary star system that consists of a red giant star and a white dwarf
locked together by gravity. These two stellar objects orbit so closely
around one another that the outer layers of the red giant are pulled
away by the intense gravitational force of the white dwarf. This
material gradually falls onto the surface of the white dwarf. Over time,
enough material may accumulate on the white dwarf to trigger a colossal
thermonuclear explosion, causing a dramatic brightening of the binary
called a nova. Astronomers saw V745 Sco fade by a factor of a thousand in optical light over the course of about 9 days.

Astronomers observed V745 Sco with Chandra a little over two weeks
after the 2014 outburst. Their key finding was it appeared that most of
the material ejected by the explosion was moving towards us. To explain
this, a team of scientists from the INAF-Osservatorio Astronomico di
Palermo, the University of Palermo, and the Harvard-Smithsonian Center
for Astrophysics constructed a three-dimensional (3D)
computer model of the explosion, and adjusted the model until it
explained the observations. In this model they included a large disk of
cool gas around the equator of the binary caused by the white dwarf
pulling on a wind of gas streaming away from the red giant.

The computer calculations showed that the nova explosion’s blast wave
and ejected material were likely concentrated along the north and south
poles of the binary system. This shape was caused by the blast wave
slamming into the disk of cool gas around the binary. This interaction
caused the blast wave and ejected material to slow down along the
direction of this disk and produce an expanding ring of hot, X-ray
emitting gas. X-rays
from the material moving away from us were mostly absorbed and blocked
by the material moving towards Earth, explaining why it appeared that
most of the material was moving towards us.

In the figure
(pictured above) showing the new 3D model of the explosion, the blast
wave is yellow, the mass ejected by the explosion is purple, and the
disk of cooler material, which is mostly untouched by the effects of the
blast wave, is blue. The cavity visible on the left side of the ejected
material (see the labeled version) is the result of the debris from the
white dwarf's surface being slowed down as it strikes the red giant.
Below is an optical image from Siding Springs Observatory in Australia.

Optical Image of V745 Sco

This image of V745 Sco (also known as Nova 1937) was taken on February 6, 2014 by S. O'Conner (OCN, St. Georges, Bermuda). Scale: 16 arcmin x 16 arcmin.
(Credit: S. O'Connor (OCN, St. Georges, Bermuda)

An extraordinary amount of energy was released during the explosion,
equivalent to about 10 million trillion hydrogen bombs. The authors
estimate that material weighing about one tenth of the Earth’s mass was
ejected.

While this stellar-sized belch was impressive, the amount of mass
ejected was still far smaller than the amount what scientists calculate
is needed to trigger the explosion. This means that despite the
recurrent explosions, a substantial amount of material is accumulating
on the surface of the white dwarf. If enough material accumulates, the
white dwarf could undergo a thermonuclear explosion and be completely
destroyed. Astronomers use these so-called Type Ia supernovas as cosmic distance markers to measure the expansion of the Universe.

The scientists were also able to determine the chemical composition
of the material expelled by the nova. Their analysis of this data
implies that the white dwarf is mainly composed of carbon and oxygen.

A 3D print of the model
was also created (pictured below). This 3D print was simplified and
printed in two parts, the blast wave (shown here in grey) and the
ejected material (shown here in yellow).

A paper describing these results was published in the February 1st,
2017 issue of the Monthly Notices of the Royal Astronomical Society and
is available online.
The authors are Salvatore Orlando from the INAF-Osservatorio
Astronomico di Palermo in Italy, Jeremy Drake from the
Harvard-Smithsonian Center for Astrophysics in Cambridge, MA and Marco
Miceli from the University of Palermo.

Friday, September 15, 2017

The galaxy is famous for containing an especially extensive HII region, a large cloud composed of ionised hydrogen (or HII, pronounced “H-two”, with H being the chemical symbol for hydrogen and the “II” indicating that the atoms have lost an electron to become ionised).
NGC 5398’s cloud is named Tol 89 and sits at the lower left end of the
galaxy’s central “bar” of stars, a structure that cuts through the
galactic core and funnels material inwards to maintain the star
formation occurring there.

Tol 86 is conspicuous in being the only large massive star forming
complex in the entire galaxy, with an extension of roughly 5000 times
4000 light-years; it contains at least seven young and massive star clusters.
The two brightest clumps within Tol 89, which astronomers have named
simply “A” and “B”, appear to have undergone two bursts of star-forming
activity — “starbursts”
— roughly 4 million and less than 3 million years ago respectively. Tol
89-A is thought to contain a number of particularly bright and massive
stars known as Wolf-Rayet stars, which are known for their high temperatures and extreme stellar winds.

Astronomers using ESO’s Very Large
Telescope have detected titanium oxide in an exoplanet atmosphere for
the first time. This discovery around the hot-Jupiter planet WASP-19b
exploited the power of the FORS2 instrument. It provides unique
information about the chemical composition and the temperature and
pressure structure of the atmosphere of this unusual and very hot world.
The results appear today in the journal Nature.

A team of astronomers led by Elyar Sedaghati, an ESO fellow
and recent graduate of TU Berlin, has examined the atmosphere of the
exoplanet WASP-19b
in greater detail than ever before. This remarkable planet has about the
same mass as Jupiter, but is so close to its parent star that it
completes an orbit in just 19 hours and its atmosphere is estimated to
have a temperature of about 2000 degrees Celsius.

As WASP-19b passes in front of its parent star, some of the
starlight passes through the planet’s atmosphere and leaves subtle
fingerprints in the light that eventually reaches Earth. By using the FORS2 instrument on the Very Large Telescope
the team was able to carefully analyse this light and deduce that the
atmosphere contained small amounts of titanium oxide, water and traces
of sodium, alongside a strongly scattering global haze.

“Detecting such molecules is, however, no simple feat,” explains Elyar Sedaghati, who spent 2 years as ESO student to work on this project. “Not
only do we need data of exceptional quality, but we also need to
perform a sophisticated analysis. We used an algorithm that explores
many millions of spectra spanning a wide range of chemical compositions,
temperatures, and cloud or haze properties in order to draw our
conclusions.”

Titanium oxide is rarely seen on Earth. It is
known to exist in the atmospheres of cool stars. In the atmospheres of
hot planets like WASP-19b, it acts as a heat absorber. If present in
large enough quantities, these molecules prevent heat from entering or
escaping through the atmosphere, leading to a thermal
inversion — the temperature is higher in the upper atmosphere and lower
further down, the opposite of the normal situation. Ozone plays a
similar role in Earth’s atmosphere, where it causes inversion in the
stratosphere.

“The presence of titanium oxide in the atmosphere of
WASP-19b can have substantial effects on the atmospheric temperature
structure and circulation.” explains Ryan MacDonald, another team member and an astronomer at Cambridge University, United Kingdom. “To be able to examine exoplanets at this level of detail is promising and very exciting.” adds Nikku Madhusudhan from Cambridge University who oversaw the theoretical interpretation of the observations.

The astronomers collected observations of WASP-19b over a period of more than one year.
By measuring the relative variations in the planet’s radius at
different wavelengths of light that passed through the exoplanet’s
atmosphere and comparing the observations to atmospheric models, they
could extrapolate different properties, such as the chemical content, of
the exoplanet’s atmosphere.

This new information about the presence of metal oxides
like titanium oxide and other substances will allow much better modeling
of exoplanet atmospheres. Looking to the future, once astronomers are
able to observe atmospheres of possibly habitable planets, the improved
models will give them a much better idea of how to interpret those
observations.

“This important discovery is the outcome of a refurbishment of the FORS2 instrument that was done exactly for this purpose,” adds team member Henri Boffin, from ESO, who led the refurbishment project. “Since then, FORS2 has become the best instrument to perform this kind of study from the ground.”

More Information

This research was presented in the
paper entitled “Detection of titanium oxide in the atmosphere of a hot
Jupiter” by Elyar Sedaghati et. al. to appear in Nature.

ESO is the foremost intergovernmental astronomy
organisation in Europe and the world’s most productive ground-based
astronomical observatory by far. It is supported by 16 countries:
Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland,
Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden,
Switzerland and the United Kingdom, along with the host state of Chile.
ESO carries out an ambitious programme focused on the design,
construction and operation of powerful ground-based observing facilities
enabling astronomers to make important scientific discoveries. ESO also
plays a leading role in promoting and organising cooperation in
astronomical research. ESO operates three unique world-class observing
sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO
operates the Very Large Telescope and its world-leading Very Large
Telescope Interferometer as well as two survey telescopes, VISTA working
in the infrared and the visible-light VLT Survey Telescope. ESO is also
a major partner in two facilities on Chajnantor, APEX and ALMA, the
largest astronomical project in existence. And on Cerro Armazones, close
to Paranal, ESO is building the 39-metre Extremely Large Telescope, the
ELT, which will become “the world’s biggest eye on the sky”.